Radio frequency identification (RFID) systems generally consist of one or more RFID readers and a plurality of RFID transponders, which are commonly termed credentials. The RFID transponder is an active or passive radio frequency communication device, which is directly attached to or embedded in an article to be identified or otherwise characterized by the RFID reader, or which is alternatively embedded in a portable substrate, such as a card, keyfob, tag, or the like, carried by a person or an article to be identified or otherwise characterized by the RFID reader. Exemplary RFID systems are disclosed in U.S. Pat. No. 4,730,188 to Milheiser (the '188 Patent), U.S. Pat. No. 5,541,574 to Lowe et al. (the '574 Patent), and U.S. Pat. No. 5,347,263 to Carroll et al. (the '263 Patent), all of which are incorporated herein by reference.
A passive RFID transponder is dependent on the host RFID reader as its power supply. The host RFID reader “excites” or powers up the passive RFID transponder by transmitting high voltage excitation signals into the space surrounding the RFID reader, which are received by the RFID transponder when it is near, but not necessarily in contact with, the RFID reader. The excitation signals from the RFID reader provide the operating power for the circuitry of the recipient RFID transponder. In contrast, an active RFID transponder is not dependent on the RFID reader as its power supply, but is instead powered up by its own internal power source, such as a battery.
Once the passive or active RFID transponder is powered up, the RFID transponder communicates information in a digital format, such as identity data or other characterizing data stored in the memory of the RFID transponder, to the RFID reader and the RFID reader can likewise communicate information back to the RFID transponder without the RFID reader and RFID transponder coming in contact with one another. The powered up RFID transponder communicates with the RFID reader by generating transponder data signals within the circuitry of the RFID transponder and transmitting the transponder data signals in the form of electromagnetic waves into the surrounding space occupied by the RFID reader. The RFID reader contains its own circuitry as well as its own reader programming, which are cooperatively designed to “read” the data contained in the transponder data signals received from the RFID transponder. It is noted that the reader circuitry and programming are typically significantly larger and more complex than the RFID transponder due to the expanded functional requirements of the RFID reader in comparison to the RFID transponder.
An essential feature of all RFID systems is that all RFID transponders and readers of a given system are sufficiently compatible to effectively communicate with one another. Compatibility is achieved in part by specifying the carrier frequency at which data signals are communicated between the RFID transponders and readers of the RFID system. There are currently two standard carrier frequencies which have been generally accepted for use in RFID systems. RFID systems, which employ RFID transponders of the type conventionally termed proximity cards or proximity tags, typically communicate by means of data signals at a carrier frequency within a range of 100 to 150 kHz. This carrier frequency range is nominally referred to herein as 125 kHz carrier frequency and is deemed low frequency. In contrast, RFID systems employing RFID transponders of the type conventionally termed smart cards typically communicate by means of data signals at a carrier frequency of 13.56 MHz, which is deemed high frequency. The frequency bandwidth available for use around the carrier frequency of 13.56 MHz is defined by industry-wide standards such as ISO standards 15693 and 14443.
At present, use of RFID transponders operating at the low carrier frequency and RFID transponders operating at the high carrier frequency have proliferated throughout the world. Therefore, it is both highly desirable and a significant challenge to develop an RFID reader which is compatible with RFID transponders operating at either accepted carrier frequency and which achieves a level of performance comparable with an RFID reader optimized to operate at a single carrier frequency. As such, the present invention recognizes a need for an RFID system having one or more RFID readers, each of which is capable of communicating with a plurality of RFID transponders, one or more of which are operating at a different carrier frequency than the remaining RFID transponders.
It is generally an object of the present invention to provide an RFID system having one or more RFID readers with multiple carrier frequency communication capabilities. It is a more particular object of the present invention to provide such an RFID reader with multiple carrier frequency communication capabilities, wherein the communication range between the RFID reader and the RFID transponders operating at different carrier frequencies is not significantly compromised by the expanded communication capabilities of the RFID reader. It is a further object of the present invention to provide such an RFID reader with multiple carrier frequency communication capabilities, which remains relatively compact despite the expanded communication capabilities of the RFID reader. It is another object of the present invention to provide such an RFID reader with multiple carrier frequency communication capabilities, wherein reader performance is essentially the same whether the RFID reader is communicating with an RFID transponder operating at the low carrier frequency or an RFID transponder operating at the high carrier frequency.
These objects and others are accomplished in accordance with the invention described hereafter.